Hello,

I have scene with some plants (many triangles) on the ground, and clouds (a
stretched box with scattering media) in the sky.

The plants alone render very fast (> 10.000 pps), and clouds alone also.
However, if I put both elements to the scene, rendering becomes very slow (< 200
pps).

I tried putting both elements in two different light_groups, such as:

light_group{ light_source{ L1} object{Plants}}

light_group{ light_source{ L2 } object{Clouds}}

but this did not help. I might add, that the lower border of the cloud-box is
much higher than the upper border of the plants. Adding "no_shadow" to both,
plants and clouds, also does not help. Photons and radiosity are also switched
off for this scene.

Any idea what's the reason for this slow-down, and what would help? To my
opinion, there should be no interaction of both, plants and clouds, during
rendering.

Thank you!

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Hello,

I found a solution: Bounding the plants in a box which does not hit the clouds
helps. However, I still don't know why ...


"Sereib" <nomail@nomail> wrote:
> Hello,
>
> I have scene with some plants (many triangles) on the ground, and clouds (a
> stretched box with scattering media) in the sky.
>
> The plants alone render very fast (> 10.000 pps), and clouds alone also.
> However, if I put both elements to the scene, rendering becomes very slow (< 200
> pps).
>
> I tried putting both elements in two different light_groups, such as:
>
> light_group{ light_source{ L1} object{Plants}}
>
> light_group{ light_source{ L2 } object{Clouds}}
>
> but this did not help. I might add, that the lower border of the cloud-box is
> much higher than the upper border of the plants. Adding "no_shadow" to both,
> plants and clouds, also does not help. Photons and radiosity are also switched
> off for this scene.
>
> Any idea what's the reason for this slow-down, and what would help? To my
> opinion, there should be no interaction of both, plants and clouds, during
> rendering.
>
> Thank you!

Post a reply to this message

> Hello,
>
> I found a solution: Bounding the plants in a box which does not hit the clouds
> helps. However, I still don't know why ...
>
>
> "Sereib" <nomail@nomail> wrote:
>> Hello,
>>
>> I have scene with some plants (many triangles) on the ground, and clouds (a
>> stretched box with scattering media) in the sky.
>>
>> The plants alone render very fast (> 10.000 pps), and clouds alone also.
>> However, if I put both elements to the scene, rendering becomes very slow (< 200
>> pps).
>>
>> I tried putting both elements in two different light_groups, such as:
>>
>> light_group{ light_source{ L1} object{Plants}}
>>
>> light_group{ light_source{ L2 } object{Clouds}}
>>
>> but this did not help. I might add, that the lower border of the cloud-box is
>> much higher than the upper border of the plants. Adding "no_shadow" to both,
>> plants and clouds, also does not help. Photons and radiosity are also switched
>> off for this scene.
>>
>> Any idea what's the reason for this slow-down, and what would help? To my
>> opinion, there should be no interaction of both, plants and clouds, during
>> rendering.
>>
>> Thank you!
>
>
>
>

The mesh for your plants may have some stray, isolated, triangles placed 
very high. Those are probably very small makint them essentialy 
invisible, showing only by accident.
If that's the case, then, your manual bounding effectively removed those.

If that's the case, doing an intersection of your mesh and a box similar 
to your bounding box should have about the same effect.



Alain

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